A battery pack may source or sink current during operation, where the amount of current may be limited due to various constraints. In order to stay within the battery pack limits, the battery pack may transmit the battery pack sourcing and/or sinking capacities to an external controller so that the external load or source that is in communication with the battery pack may adjust operation of the load or source to accommodate the battery pack limits. In addition, the battery pack current sinking and/or sourcing limits may be imposed via hardware. For example, fuses may be placed between battery cells and an external load or source to limit current flow into and out of the battery pack. Thus, degradation of a battery pack may be limited by way of a combination of hardware and software. However, accessing the battery pack to replace a blown fuse can be cumbersome. Furthermore, a load or source external to the battery pack may not have the capacity to precisely follow battery limits as desired during periods of degradation, or during transient operation. Further still, the degree to which the current limits are imposed may depend on the operating conditions, including the duration over which the over-current conditions persists and the degree to which the current is over the prescribed limit.
The inventor herein has recognized the above issues and developed various approaches to address them. In one approach, a method for controlling output of a battery pack, comprising: opening a contactor that electrically couples said battery pack to an electrical circuit external of said battery pack when an integrated variable or parameter related to a tracked variable of the battery pack exceeds a threshold amount, the integrated variable or parameter integrated when the tracked variable of said battery pack is greater than a threshold amount.
By opening a contactor that electrically couples a battery pack to a circuit that is external to the battery pack when an integrated amount of current of the battery pack exceeds a threshold level, it is possible to reduce the possibility of battery pack degradation without having to access the battery pack and replace a fuse. In particular, a contactor can be controlled in response to an output of a current sensor. For example, during periods when a battery is operating within prescribed limits the contactor can be controlled in response to requests to operate a vehicle. However, if the current entering or exiting the battery exceeds a threshold amount of current, the amount of current exceeding the threshold may be integrated. When the value of the integrated current exceeds a threshold the contactor may be opened. In this way, current flow into and out of a battery pack may be controlled without having to rely on a hardware fuse or an external controller. Further, the approach correlates the degree of over-current operation to the duration of that condition, in that current may be allowed to go slightly over limit for a long duration before opening the contactors, whereas current may be allowed to go significantly over limit for only a short duration before opening the contactors. In this way, it is possible to take advantage of the interrelationship between the degree and duration of over-current operation. Such an approach can reduce unnecessary contactor opening and thereby reduce intervening in drive operation. As some applications may be more prone to longer, but lower, over current conditions, while other applications may be more prone to shorter, but higher, over current conditions, the above approach accommodates both conditions and various combinations therebetween.
The present description may provide several advantages. In particular, the method can reduce battery pack degradation without having to replace hardware or rely on external systems. Further, the present description provides for additional measures of battery pack degradation protection. Further still, the level of threshold currents can be adjusted for different capacity battery packs without having to change hardware or software. Further still, the level of threshold currents may be changed dynamically with battery temperature, charge level, or age.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.